In the electrostatic printer or electrostatic plotter, the printing is carried out by forming an electrostatic latent image on an electrostatic recording sheet by using a multiple-needle electrode head, developing the latent image by using a toner and then fixing. The multiple-needle electrode head which is used in such an apparatus is made by forming a large number of recording electrodes on front and back surfaces of an electrode substrate, molding the substrate by an epoxy resin or the like and polishing for finishing its front edge, as disclosed, for example, in JP-A-53-20929, JP-A-56-110959, JP-A-56-122056, and co-pending U.S. patent application Ser. No. 07/634,608 filed on Dec. 27, 1990 now U.S. Pat. No. 5,107,283.
In case of a double-row multiple-needle electrode head which is used in a large electrostatic plotter, for instance, in an apparatus for printing on a sheet of the A0 size, a width in the longitudinal direction of an electrode substrate is about one meter and about 7200 needle-shaped recording electrodes (hereinafter, also simply referred to as electrodes) on each side, or total 14400 electrodes are formed in parallel on both of the front and back sides. When the electrode substrate is large as mentioned above and the electrodes are formed by a technique such as plating or etching, it is difficult to make the width of the electrode pattern uniform in the formation of the electrodes. In addition, since the electrodes are formed at a predetermined very fine pitch such as 0.127 mm, the rate in generation of defects such as short-circuit between the electrodes and breakage of the electrodes, becomes high. Moreover, even if only one of a large number of electrodes is defective, the whole electrode substrate is regarded as a defective article. Consequently, the conventional multiple-needle electrode head involves a problem that the manufacturing of the same is extremely difficult and a yield is low.
In case of the multiple-needle recording head using an electrode substrate having a length of one meter, it is impossible to process such a long electrode substrate by conventional plating apparatus, exposing apparatus, or the like. To form such a long electrode substrate, therefore, it is necessary to make large the size of processing apparatus such as plating apparatus, exposing apparatus or etching apparatus, resulting in high production cost.
Further, in order to obtain a highly precise recording image, the electrode substrate is required to have a highly accurate linearity in its longitudinal direction. However, as the length of electrode substrate becomes larger, it becomes more difficult to realize the highly accurate linearity.